1. Field of the Invention
The present invention relates to a lens barrel such as a photographing (imaging) lens which incorporates a rotatable ring performing an advancing/retracting operation in which the rotatable ring moves along an optical axis while rotating, and a fixed-position rotating operation in which the rotatable ring rotates at an axial fixed position without moving along the optical axis.
2. Description of the Related Art
Retractable photographing lenses in which a rotatable ring such as a cam ring advances along an optical axis while rotating from a fully retracted position toward a ready-to-photograph position (e.g., zooming range of zoom lens) upon power being turned ON and in which the cam ring stops advancing upon reaching the ready-to-photograph position to be rotatable at an axial fixed position on the optical axis without rotating are known in the art. In such known retractable photographing lenses, a drive mechanism for driving the rotatable ring is generally complicated and large in size. In the case where the rotatable ring can be rotated to a predetermined angular position (such as an assembling/disassembling position) outside a normal range of rotation of the rotatable ring, the photographing lens needs to be provided therein with a stop device for preventing the rotatable ring from rotating to the predetermined angular position in a normal operating state of the photographing lens. However, in the case where the rotatable ring is a type which performs an advancing/retracting operation in which the rotatable ring rotates while advancing or retracting along the optical axis, and a fixed-position rotating operation in which the rotatable ring rotates at a predetermined axial fixed position without moving along the optical axis, the structure of the stop device is generally complicated; moreover, it is generally difficult to make the stop device operate properly.